Our circadian rhythms keep us in tune with the day. Some of the molecular signals that implement and regulate the circadian rhythm have been identified, but the complexity of the various systems affected by circadian rhythms is not well understood. Many people work against their circadian clock, whether it be a scientist who hops seven time zones eastward and still hopes to be awake at a conference session with the lights dimmed, or someone who works the night shift and needs cognitive acuity and physical dexterity during the hours when most of us are asleep. To further understand how disruption of the circadian rhythm affects us, Karatsoreos et al. studied mice kept in an unnaturally short day/night cycle. With a cycle of 20 rather than 24 hours, the mice showed a variety of disrupted responses. They gained weight, had elevated insulin levels, and demonstrated reduced cognitive flexibility. Neurons in the brain's cortex showed reduced complexity. Study of these mice may help us understand, for example, the unexpected incidence of obesity among shift workers.